56 



ORGANOGEAPHT. 



132. 



appendages are, therefore, simply modifications of steUate hairs. 

 A scale may be defined as a flattened membranoiis more or less 

 rounded plate of cellular tissue, attached by its centre, and 

 presenting a more or less irregular margin from the unequal 

 prolongation of its component cells (/^. 128). These scales are 

 particularly abundant on the surface of some plants, to which 

 they communicate a scurfy or silvery appearance, as in the 

 Elcsagnus, &c. Such a surface is said to be lepidote, from lej)is, 

 the Greek term for a scale. 



Other modifications of hairs which are allied to the above, are 

 the ramenta or ramentaceous hairs so abundant upon Ferns ( Hg. 

 129). These consist of cells {fig. 130) combined so as to form a 

 brownish flattened scale attached by its base to the surface of the 

 epidermis from whence it grows. 



When the hairs are composed of cells which are short, and 

 have their sides thickened by secondary deposits so that they 

 form stiffened processes, they are then called seta or bristles, and 

 the surface is then termed setose or setaceous. These slightly 

 modified, form prickles, which may be defined as large hardened 

 processes terminating in a sharp point and springing from the 

 epidermis or the bark of plants {fig. 131). They are especially 

 abundant on the stems of the Kose and Bram- 

 ble. These must be distinguished from spines,, 

 to be hereafter described when speaking of 

 branches. 



The hairs above described commonly contain 

 fluid of a watery nature, which may be colour- 

 less or coloured. Such have been termed Igm- 

 fhatic hairs, to distinguish them from other hair- 

 like appendages which are filled with special se- 

 cretions, and which have heeji CdlleA glandular 

 hairs. The latter will be again alluded to under 

 glands, to which variety of epidermal appendage 

 they more properly belong. 



Hairs occur upon various parts of plants, and, 

 according to their abundance and nature, they 

 give varying appearances to their surfaces, all 

 of which are distinguished in practical botany 

 by special names. The more common position 

 of hairs is upon the leaves and young stems, but 

 they are also found on the parts of the flower, the 

 fruit, and the seed. The substance called eow- 

 hage or cowitch consists of the hairs covering 

 the legumes of Mticuna pruriens ; while cotton 

 is the hair covering the seeds of various species 

 of Gossypium. Cotton may be readily dis- 

 tinguished under the microscope from the liber-cells already 

 described, from its component cells not possessing any stiff 



FU}. 132. a. Cotton 

 b. Flax fibres. 



